Production of peptides by recombinant techniques using either prokaryotic or eukaryotic expression systems inherently yields the peptide with a leading methionine amino acid. This amino acid may not be present in the native protein i.e. the variant of the peptide processed for translocation. Obtaining the peptide without the leading methionine thus requires a further processing step. In the present invention the step is performed by the enzyme Methionine Aminopeptidase, which selectively cleaves the initiator methionine from the peptide.
Methionine Aminopeptidases (Met-AP's) are known in the art as enzymes which cleaves leading methionines, if the leading peptide sequence is of a certain predetermined character. Wild-type Escherichia coli Met-AP selectively cleaves after an initiator Met residue if the residue in the P1′ position is Gly, Ala, Ser, Thr, Pro, Val or Cys.
In the present invention the methionine aminopeptidases are improved by introducing mutations in the substrate binding sites which results in methionine aminopeptidases which cleaves the methionine regardless of the leading peptide sequence (P1′ position)